As an electrical engineer, I can deal with the problem of not finding the thing I want. If it doesn’t exist, I make it myself.
The question about 18650 cells is a good one. They are available, but it’s not recommended to change them yourself, as the cells can catch fire. The problem is one of liability.
Check out http://www.batteryspace.com. I get my Li-ion packs from them. They make you sign off all sorts of disclaimers about liability before accepting your money.
